Labyrinth seals are commonly used to provide a seal, and therefore minimize fluid leakage, between static and rotating parts in turbomachines, such as axial flow gas turbines or steam turbines.
A conventional labyrinth seal for sealing between the tips of moving blades and the radially adjacent static casing in an axial flow turbine is illustrated in FIG. 1 of EP 1001139 A1. In this conventional labyrinth seal, axially spaced and circumferentially extending sealing fins are caulked into the static casing and project radially inwardly, across the fluid flow path, towards castellated arcuate blade shrouds at the blade tips. A radial clearance is normally provided between the tip of each sealing fin and the radially adjacent arcuate blade shrouds to prevent or minimize rubbing contact between the tips of the static sealing fins and the moving blade shrouds during radial excursions of the moving blade shrouds relative to the radially adjacent static casing.
In conventional labyrinth seals such as that shown in FIG. 1 of EP 1001139 A1, axially flowing working fluid can escape through the radial clearances provided between the tips of the sealing fins and the radially adjacent arcuate blade shrouds, thus reducing the effectiveness of the labyrinth seal.
It is, therefore, desirable to provide labyrinth seals with improved sealing capability.